Sometimes it is desirable to be able to quickly change radiation direction of an antenna. In other words the antenna lobe is to be quickly shifted or swept between different directions. The demand regarding time is often such that an arrangement for mechanical motions of the antenna is not feasible.
Today antenna arrays are used which contain elements in which a signal phase at each element may be individually set to achieve a control of the main direction of the antenna lobe. Another technique to achieve a control of a radiation lobe is to utilize what is normally referred to as an "optical phased array", which includes an adaptable lens which, for instance, is disclosed in a document U.S. Pat. No. 5,212,583. This document describes a device utilizing a single plate of a material presenting ferroelectric properties. In a second embodiment disclosed the ferroelectric plate is provided with a ground-plane on one side and two orthogonal grids on the other side for radiation lobe control. Both the grids and the ground-plane are made in a light transparent material, indium/tin oxide. This document only refers to optical systems and does not discuss whether this is applicable to the microwave range.
However, in a microwave system, when the wavelength of an electromagnetic wave generally is much larger than the distance between conducting grid wires, it should be noted that only a grid wire direction being perpendicular to the E-field vector of the propagating wave can be utilized for controlling the refractive index of the ferroelectric plate. A grid wire direction parallel to the E field vector will result in a reflection of the electromagnetic wave. In the disclosed optical system the grid conductor wire distances are expected to be much larger than the wavelength of the light, i.e. .lambda.&lt;&lt;wire separation. Besides a conducting ground-plane will totally reflect the propagating microwave.
Two documents U.S. Pat. Nos. 4,706,094 and 4,636,799 both disclose a ferroelectric block between grids of parallel wires. According to the first document only controlling fields are used across the block, i.e. in the propagation direction of the wave. According to the other document the voltages at the wires are arranged such that the field may adopt arbitrary directions in the plane perpendicular to the wires. In the first document it is pointed out that the "normally" high conductive wires only transmits perpendicular, linear polarization but that they may be replaced by resistive wires being able to transmit also parallel polarization at some loss.
WO,A1,93/10571 demonstrates a development of U.S. Pat. No. 4,636,799 where only fields perpendicular to the wires are used. Here only one layer of wires is needed and the ferroelectric material has been divided into a plurality of blocks such that the grid of wires can be disposed in the middle of the ferroelectric layer.
However it will be noted that, the documents cited above are addressing the use of highly conductive wires and a voltage gradient is then achieved by applying different voltages to the individual wires according to a given pattern. Furthermore the devices described are related to utilizing the ferroelectric material for "electro-optic lenses" which primarily directs the utilization to frequencies corresponding to electromagnetic radiation in the nanometer range.
Furthermore none of the documents has disclosed a device being able to scan microwave radiation in two orthogonal planes in a single ferroelectric plate. Neither it has been shown that this can be done by using several layers of ferroelectric material without losses.
Therefore there is still a demand for a method and a device, which will operate even at a much lower frequency range, i.e., in the microwave range.